1. Field of the Invention
The present invention relates to bath shakers and, more particularly, to machines having means for vibrating a plurality of vessels while they are immersed in a liquid bath.
2. Description of the Prior Art
In the field of chemical and biological testing and research, it is often necessary to mix a number of substances together by placing the substances in a vessel and then shaking the vessel for an extended period of time. Rotary shaker machines have been widely used in the past for this purpose. Such shakers typically include one or more shelves on which are fixed a plurality of vessel-mounting clamps for holding such laboratory items as flasks, bottles, beakers, etc. The shelves are moved by a drive mechanism so that the contents of the vessels are agitated. A typical drive mechanism includes an eccentrically driven shaft on which a frame is mounted for supporting the shelves. In response to operation of the drive mechanism, the shaft causes the frame to gyrate, orbit or otherwise move thereby causing the shelves and vessels to shake. Descriptions of conventional shakers can be found in the following U.S. Pat. Nos.: 4,750,845; 4,747,693; 4,673,297; 4,109,319; 4,047,704; 3,430,926 and 3,220,704.
In some cases it is also desirable that, while the mixing is being performed, the substances be maintained at a particular temperature. To accomplish this, the vessels in which the substances are mixed are often immersed in a temperature-controlled liquid bath. To ensure that the substances are thoroughly mixed or kept in suspension with each other, the vessels are continuously shaken while they are immersed in the bath. Machines, called bath shakers, are available for performing this task.
Bath shakers typically include a tank for holding a water bath, a heater or cooler for maintaining the water at some predetermined temperature, a shelf for supporting the mixing vessels while immersed in the water, and a shaker for orbiting the shelf. U.S. Pat. No. 3,601,372 illustrates the structural details of a typical bath shaker. Additional prior art bath shakers and their drive mechanisms are illustrated in Catalog S28730BP, "Biological Shakers", published by New Brunswick Scientific, Edison, N.J.
As is evident from these references, developers of bath shakers have long recognized the need for making improvements to the drive mechanisms thereof. For example, the '372 patent describes a shaker wherein a shelf, a triple-eccentric drive mechanism and a first permanent magnet are mounted in a water bath. A second permanent magnet, mounted external of the water bath, is rotated by a motor to produce a rotating magnetic field that drives the first magnet. In turn the first magnet drives the triple-eccentric mechanism which in turn causes the shelf to orbit. The drive mechanism of the '372 shaker does not require the use of structures that must pass through the walls of the water bath. As such, the principles of the '372 patent have been successfully used to construct leakage-free bath shakers. However, one disadvantage with a '372-type shaker is the location of the triple-eccentric drive mechanism in the water bath, requiring the use of expensive waterproof bearings.
The water bath shaker shown on page B-34 in the New Brunswick Scientific Catalog S28730BP, referred to therein as Model G76, has a triple-eccentric drive mechanism that is mounted external to and below the water bath. Four arms extend outwardly from the drive mechanism, up and around the exterior of the bath-shaker housing, and over the upper edges of the housing where they terminate on either side of the shaker above the water bath. A vessel-carrying shelf has four rigid vertical hangers that are attached to the arms for suspending the shelf in the bath.
The G76 bath shaker is an improvement over the device of the '372 patent in the sense that the entire drive mechanism, including the triple eccentric, is mounted external of the water bath. However, the external arms of the G76 shaker are in some cases a disadvantage since they increase the exterior size of the overall device which in turn increases the amount of linear bench space occupied by the bath shaker. Other conventional bath shakers with external arms are the Lab-Line Model 3545, as shown on pages S-11 of the brochure LAB-LINE SHAKERS, and the Bellco Sci/ERA Water Bath Shaker.
U.S. Pat. No. 4,923,305 discloses still another type of bath shaker. The shaker of the '305 patent has a tub in the form of a closed circular ring with a central passage for a drive shaft. A shelf, essentially constructed as a circular ring, is mounted at the upper end of the drive shaft so as to be immersed in the water while agitated by the drive shaft. Although the '305 shaker does not include external arms, its circular shape is an equally inefficient contour in utilizing linear bench space. An implementation of a circular shaker is illustrated as model "HT, Aquatron Waterbath Rotary Shaker" in a brochure, YP251284e, published by INFORS AG, the assignee of the '305 patent.
Other shakers of general interest are produced by Adolf Kuhner AG of Switzerland and by GCA Corp. of Chicago, Ill.
Although there has been a long recognized need for improvements in several bath shaker features, no prior art device has been devised that resolves many of the current shortcomings. Ideally, an improved bath shaker would be shaped to occupy a minimum of linear bench space, thereby increasing the number of devices that may be placed side-by-side; would be easy to repair, maintain and clean; would include a simple, efficient drive mechanism wherein all bearing surfaces are quiet, smooth and substantially isolated from the water bath; would have a relatively large capacity; and would operate efficiently with little or no adverse splashing at high speeds and during start up. The present invention fulfills this need.